The Impacted Mandibular Canine

Published: May 2015

Bulletin #44 – May 2015

The
Impacted Mandibular Canine

Impacted mandibular canines have been the subject of many
published journal articles and, for the most part, the articles have described
the condition for its oddity/curiosity/rarity/freaky/quirky value, rather than satisfying
the patient’s hope that something constructive may be done about it.

In terms of etiology, very little is known about the mandibular
canine that exhibits intraosseous migration in a more or less horizontal
direction, but it seems largely agreed that the potential for an exaggerated
degree of migration is an attribute of this tooth, to the virtual exclusion of
all other teeth in the mandible, with the possible exception of the second
premolar. The tooth will usually travel mesially and will transmigrate over the
midline symphysis to the opposite side by as much as 30mms from its normal
location, in the more extreme examples. Its occurrence is unilateral in the majority of reported cases. On the
other hand there are cases where a potentially normal eruption path of the
canine may have become deflected by the presence of a supernumerary tooth or
odontoma or a soft tissue pathologic entity, such as an apical granuloma or
dentigerous/radicular cyst related to a non-vital deciduous tooth (Fig. 1).

As one who sees many patients for treatment of the infinite
array of incarnations that tooth impaction may display, I occasionally see
patients with impacted or transposed or transmigrated mandibular canines who
are seeking treatment. As with most of my colleagues, I turn some of these
patients away with a referral for extraction to the oral and maxillofacial
surgeon, but there are a few whom I accept for treatment, with the view to
achieving an acceptable result, with the full complement of teeth. So, what are the special circumstances that
will commit so many of them to the trash can and which are the few that deserve
conservative orthodontic treatment?

Fig. 1b. A panoramic film taken 3 years later shows the
development of a dentigerous cyst displacing the permanent unerupted canine.

Prevention and interception:

Canines that are discovered moving past the root of the
lateral incisor and on towards the midline, in the complete absence of any
pathologic entity, appear to be the least likely to respond to interceptive
measures, such as the extraction of the deciduous canine and deciduous first
molar. However, follicular enlargement seems to be often associated with a
migrating unerupted canine (Fig. 1). When the same deciduous teeth are
extracted, without resolving the follicular enlargement, it again seems likely
that the migrating canine will continue on this course undisturbed, probably
because cystic change (a.k.a. follicular enlargement) is responsible for some
extreme tooth displacements.

When the enlargement of the follicle can be related to the
presence of a granuloma of a non-vital deciduous canine or first molar, these
teeth should be extracted (Fig. 2). If, at the same time, surgically initiated
rupture of the follicle by creating a window in the follicle and then
maintaining the patency of the opening with a surgical pack, the pathologic
entity will effectively be eliminated. This is because the epithelial lining of
the opened follicle metaplases to become contiguous with the oral mucosa during
its healing process1. In this situation, one may usually expect to
see much spontaneous improvement in the orientation of the tooth in a very
short time (Fig. 2).

Limiting technical factors:

A labially impacted canine is generally located in the
sub-apical depression between the labially angulated anterior border of the alveolar
ridge and the prominence of the chin (Fig. 3a, b). Although it lies on the
labial side of the incisor roots, it is usually in a direct vertical line with
the cervical margins of the incisor teeth or even lingual to that line. This
means that erupting this tooth vertically can only be performed if space is
made in the dental arch immediately above it. The roots of the adjacent
incisors prohibit the tooth from being erupted mesial or distal to that
directly vertical line without it simultaneously being drawn labially away from
these roots and the ridge.

To move the tooth labially, it is necessary to position the
arm of a custom-designed spring (Fig. 3c) on its labial side with its active
position tightly held against the surgically exposed tooth. The deeper down the
tooth, the greater will be the irritation that this spring causes to the oral
mucosa of the inside of the lip and the depth of the labial sulcus (Fig. 3d, e)and
this factor alone may create an intolerable situation for the patient. If box
loops are used, then the double loop design will cause an even greater soft
tissue impingement.

To reduce the degree of irritation, an eyelet placed on the
distal aspect of the crown of the canine will fare much better, but it will
only permit distal tipping of the canine. This is fine for a canine whose apex
is in the correct location, but not so when there is a total transposition
between the canine and the lateral incisor. Of course, irritation of the lip
tissue will also be reduced if the canine is not moved labially to a sufficient
degree, but if distal movement is performed under these circumstances, the
incisor will lose its labial cover of bone.

It is therefore reasonable to conclude that apex location in
the mesiodistal plane, depth of the tooth in relation to the depth of the
sulcus and the distance that the tooth has migrated are all factors that need
to be taken into consideration in deciding whether to attempt its resolution.

There are two major problems with viewing and diagnosing the
3-dimensional positions and relations between the roots of the canine and the
lateral incisor, which are usually evaluated using a panoramic radiograph. This
film is enormously valuable in general, but in the present situation it
presents an over-simplified picture (Fig. 3a). By flattening out its depiction
of the circular form of the anterior portion of the jaw into a 2D picture, a
displaced canine may look alarmingly simple because the curve will be lost.
Secondly, when a deeply impacted labial canine superimposes on the lateral
incisor in the narrow width of the lower jaw, the root of the incisor will be
markedly displaced lingually and, often distally, to create a partial or total
transposition between the two.

Because the canine requires to be moved around the dental
arch, labial to the roots of the incisors, it is highly likely that the tooth
will lose much of its own labial alveolar bone and soft tissue cover, as it is
drawn to its ideal location and will arrive there presenting a very long
clinical and reduced bone support (Fig. 3g). Its long term prognosis will
therefore be compromised. Simultaneously, it may cause resorption of the labial
bony cover of the incisor roots, as it goes.

The following is a list of factors that need to be
considered before attempting to attempt the orthodontic treatment of the
labially impacted mandibular canine:-

1.Depth of labial sulcus and its
relation to the depth of the canine

2.Position of apex of the
canine

3.How far has the tooth
traveled mesially?

4.How far lingually has the
incisor root been displaced?

5.Curvature of the arch

6.How much bone will remain
to cover the incisor roots following movement of the canine?

Case 1 – prevention is better than cure.

Fig. 2a. A panoramic view of a young boy with a large
radicular cyst initiated by the periapical granuloma from the non-vital
deciduous first molar. Note how the cyst has pushed the canine mesially and
inferiorly and the first premolar horizontally and inferiorly.

Fig. 2b. Following extraction of the deciduous canine and
first molar, together with drainage of the cyst, the canine and premolar have
erupted and spontaneously uprighted, with space maintenance only.

A 9 year old boy was referred to me by his pediatric dentist
and an orthodontist because of swelling of lower left side of the face. He had
a history of much dental caries of the deciduous dentition and several
restorations had been performed, including the root canal treatment of the
deciduous left mandibular canine. The panoramic radiograph (Fig. 2) revealed the
presence of a large radiolucent area under the deciduous left first molar,
which enveloped the early developing and unerupted first premolar, which was
tipped mesially 90 degrees in the horizontal a-p plane. The neighboring
unerupted permanent canine was strongly mesially tipped, apparent

ly being
“pushed” by the body occupying the large radiolucent area.

The working diagnosis of the radiolucent area was a
dentigerous cyst, caused by irritation of the dental follicle of the canine or,
alternatively, a radicular cyst arising from the rests of Malassez in the
apical granuloma from the non-vital deciduous first molar. In either case, the
enlarging cyst would undoubtedly be the prime suspect in the alteration of
eruption path of the permanent canine. The deciduous canine and the deciduous
molar were extracted and the cyst itself was opened to the oral environment
(marsupialization). A small pack was placed over the area and sutured into
place, in order to prevent the wound from healing over and left for only a
week. A simple lingual arch space maintainer was then placed.

When the patient was seen 2½ months later, the formerly
horizontal premolar was seen to be erupting mesially. A periapical radiograph
showed considerable improvement in the
orientation of their long axes. At a subsequent visit, 8 months later and 10
months after the surgical episode, both teeth had erupted. The premolar had
uprighted a full 90 degrees and the canine had over-uprighted by 50 degrees and
now stood at a 5 degree tip to the distal!

What was the key here?

1.Seeing the condition early,
with a relatively modest degree of displacement

2.Recognizing the lesion as a
cyst

3.Knowing that
marsupialization causes contraction of the dislocated teeth towards the middle
of the former void and regeneration of bone behind the former cyst lining.

Could success have been predicted? Yes, to a fair degree of
certainty.

Case 2 – This is what the macho orthodontist
might do. Would you call this success?

Fig. 3a. A panoramic view of the transmigrated left permanent
canine, beyond the mandibular midline and below the level of the incisor
apices.

Fig. 3b. A true occlusal view of the incisors shows the
canine to be labially impacted, with its root apex in the normal location.

The patient was a 14 year old male with a class 2 division 1
malocclusion. The teeth in the maxilla were treated using a headgear and
routine alignment. In the mandible,
there was an over-retained deciduous left canine, with reduced space to
accommodate the permanent canine. The initial panoramic radiograph (Fig. 3a) showed
the deciduous canine to have lost virtually all its root to resorption, but
with the presence of a supernumerary tooth apical to it. The height of the crown
of the permanent canine was seen to be slightly apical to the roots of the
incisors and at an orientation 30 degrees to the horizontal plane. Its crown
tip had already transmigrated across the midline suture, to the distal edge of
the right central incisor root. Its root apex was situated in its ideal antero-posterior
location, but very close to the lower border of the mandible.

It was a long time ago and I was that macho orthodontist.
This was my case and I was going to show ‘em!

From a naïve glance at the panoramic view, I reasoned that
the orientation of the tooth in the antero-posterior plane and the fact that
its apex was in the desired location, provided an excellent opportunity to
simply push the crown back over the midline and distally in a wide tipping
movement towards its place in the arch, with the root apex as the fulcrum of
this planned arc of circle movement. Its very depth in the mandibular bone,
below the incisor apices would be an advantage in facilitating the movement. Space
needed to be made for the tooth and this was achieved using class 3
intermaxillary elastics and a coil spring in the immediate area.

Before I started, I recognized that the tooth was below the
depth of the labial sulcus and that it had to be brought labially away from the
incisor roots before the distal swing could begin. It was clear to me at the outset
that I would need an active mechanism that would not ulcerate the very mobile
oral mucosa that invested the labial surface of the alveolus and its opposing
oral mucosa covering the inside of the lip – not to mention the connecting oral
mucosa in the depth of the sulcus trough. It had to be very delicate, applying
a light force with a good range of movement to obviate the necessity for
frequent visits and adjustments (Fig. 3c, f).

Fig. 3d. A full flap exposure is performed to reveal the
crown of the canine in the depth of the sulcus. Not the relative lack of labial
bone over the incisor roots.

Fig. 3e. An eyelet attachment is bonded to the canine
crown and the surgical flap is fully replaced. Activation of the auxiliary
spring is made by ensnaring the horizontal loop of the auxiliary archwire in
the twisted steel ligature from the eyelet immediately following the
re-suturing of the flap (not shown).

Fig. 3f. Seen 3 weeks later and following much healing,
the vertical and active mode of the auxiliary spring can be seen.

Surgery was performed under local anesthetic by the then head
of surgery in the OMFS department, Prof. Arye Steyer, who opened a full flap down
into the chin area, before we saw the tooth (Fig. 3d). Access was in fact very
easy for him and, while he retracted the flap and maintained a dry field, I
bonded the eyelet attachment with a twisted 0.012” steel ligature as the
connector (Fig. 3e). He then re-sutured the flap to its original place – given
the deep location of the tooth vis-à-vis the sulcus depth, there was no way
that this exposure could have been performed as an open procedure. Had a non-flap
window technique been used to expose the tooth, control of bleeding would not
have been adequate to permit successful attachment bonding. Only the long
twisted ligature protruding through the base of the replaced oral mucosa flap
was visible when he had finished.

Prior to the commencement of the surgical procedure, I had
already placed the prepared full arch auxiliary archwire in piggy-back style
over the heavy base arch (Fig. 3c). The auxiliary was held in place with
elastic modules, with the active loop which had been prepared for the canine
lying horizontally unattached, in its passive position. This did not interfere
with the surgical field and its presence permitted me to ensnare its terminal
helix with the shortened and hooked end of the twisted ligature in just a few
seconds at the end of the surgical procedure (Fig. 3f).

A glance at the photographs taken during the surgery will
reveal how little bone covered the roots of the incisors on the labial side,
even before traction had been initiated.

Fig. 3g. In the final stages of alignment, an auxiliary
torqueing arch is placed over the main arch top correct the position of the
canine and premolar roots.

The canine was erupted and drawn labially and distally as
planned, towards the assigned canine location. The labial movement had to be
very limited to avoid erupting the tooth into the body of the lip tissue but,
nevertheless, the tooth arrived to its destination well outside the bony
envelope and required considerable lingual root torque, in the final stages.
This resulted in a very long clinical crown and a periodontal attachment of
oral mucosa, rather than of attached gingiva (Fig. 3g). Additionally,
periapical and panoramic films taken in the final days of active treatment
showed a very significant degree of apical root resorption of many of the teeth
in that jaw (Fig. 3h, i) In the 1 year follow-up photographs, a degree of
labial relapse of the tooth was obvious.

Fig. 3h. Periapical views of the incisors, canine and
premolars show the considerable degree of apical root resorption, following the
long period of treatment and associated root movements.

Fig. 3i. A panoramic view at the end of treatment shows
the achieved root parallelism, but also resorption in several other teeth.

Fig. 3j. Seen a year post-treatment, note the long
clinical crown of the canine and the degree of positional relapse of the
canine.

Surgically, the attempt was successful, orthodontically it
was partially successful, but periodontically it was a failure. All-in-all a
pyrrhic victory because “the strength of a chain is measured only in its
weakest link”.

Case #3 – turning adverse (pathologic)
conditions to advantage

This case is still in the treatment planning stage and orthodontic
treatment has not yet commenced. Initially, on the basis of the panoramic
radiograph, the case appeared similar to case #2 in this presentation. The
patient was 12 years of age male with a spaced dentition and with all four
second molars erupted. The maxillary second deciduous molars were still
present, but about to be shed and the second premolars and permanent canines in
the maxilla were clearly about to erupt.

The right mandibular canine was impacted labially and had
transmigrated about 3mm over the midline, superimposing on the apex of the left
central incisor. Its own root apex was vertically below its ideal mesio-distal
location, in the compact bone of the lower border of the mandible and its
apex-crown long axis was at a 30 degree angle to the horizontal plane. The
crown was enveloped by an enlarged follicle (a.k.a. small dentigerous cyst).

Fig. 4a. This patient was seen at an early stage and the
abnormal orientation of the canine, with its follicular (dentigerous) cyst, was
diagnosed. The deciduous canine and first molar were extracted in the hope that
the tooth would self-correct. However, nothing was done regarding treatment for
the follicular cyst.

Fig. 4b. Seen 16 months later, the canine has continued
in its former direction and has transmigrated over the midline.

The referring orthodontist informed me that the deciduous
first molar and canine teeth had been extracted in the immediate area 16 months
earlier, in the hope that this would encourage the tooth to alter its eruption
path(Fig. 4a, b). The earlier panoramic view was produced and it showed that
there were potential developmental problems
related to all four canines. The left mandibular canine and both maxillary
canines were unerupted at the time and each had a moderately enlarged follicle.
These teeth erupted spontaneously during the period of observation, despite the
potential for eruption disturbance. The right mandibular canine follicle was
larger than the others at this time and the tooth was the only one with an
abnormal eruption path. However, its apex-crown long axis was about 50 degrees to
the horizontal and it was barely overlapping the distal side of the right
incisor root and still some way from the midline.

It is arguable that this tooth would not have transmigrated
over the midline nor would the orientation of its long axis have become more
horizontal, had the follicle had been opened (marsupialized), drainage
established and its patency maintained to prevent recurrence. On the contrary,
it may be justifiable to go so far as to suggest that there would probably have
been some spontaneous improvement in its orientation and, perhaps, even a small
chance of autonomous eruption of the tooth into the mouth, as we have seen in
case 1 above.

In consultation with the patient and his parent, it was
recommended that the tooth be extracted, because of the considerable likelihood
that a periodontal failure would accompany an orthodontic and surgical success,
as in case #2. Nevertheless, it was decided to perform a cone beam CT of the
immediate area, to complete the imaging process and to provide the case with a
full 3D basis upon which to justify the decision.

Fig. 4c, d. The CBCT axial and 3D screen shot views of
the tooth show it to be enclosed in a large follicular (dentigerous) cyst,
which has displaced it labially away from the alveolar ridge and improved its
access to biomechanical means of orthodontic correction.

The CBCT views showed that the tooth was enclosed within a
large dentigerous cyst, which had additionally displaced it labially, away from
the roots of the incisors (Fig. 4c, d). Superimposition of the canine over the
roots only involved the last millimeter of root apex, due to the depth of the
canine crown. At that level, it can be seen that the apical third of the root
was covered on its labial side only by the external surface of the sac lining
of the cyst, with no bone intervening. Moreover, these roots were situated
within a crater carved into the labial alveolus by the presence of the expanded
cyst. Thus, from this labial location,
2-4mms labial to the alveolar bone, tipping the tooth distally around the arch
would appear to be a justified approach that appears to have a better prognosis
than was first thought, from viewing only the panoramic view. Additionally,
with resolution of the cyst, it can be reasonably expected that the lack of
bone over the incisor apices will be compensated by new bone filling in the
resorption crater, on their labial aspect1.

Case 4- ….. with the best intentions in the
world!

Fig. 5a. Periapical views of the transposed order of the
lateral incisor and canine teeth. Note that the root apices of the two involved
teeth are also completely transposed. It is impossible to correct the order of
these teeth within the narrow alveolar rim of bone, without creating serious
periodontal problems, including long clinical crowns, gingival inflammation and
recession and loss of bone support.

The case involved a 15 year old female who had been in
orthodontic treatment by a general dentist for several years for the correction
of a severe mandibular left canine-lateral incisor (Md2C)
transposition (Fig. 5a).

Fig. 5b. The orthodontist attempted to reverse the
abnormal order. The illustration shows different views of the condition when
first seen for re-evaluation of treatment. It was considered that extraction
would be the most appropriate line of treatment at this point. Note the extreme
labial ectopy and uncontrolled mesio-labial rotation that has occurred due to
elastic traction direct to a labial bracket and the degree of gingival
inflammation and gingival recession present.

The lateral incisor had been moved into interproximal
contact with the central incisor and the canine had been surgically exposed and
attachment bonded. The canine was then extruded occlusally and tipped distally
to circumnavigate the lateral incisor on its labial side. Neither the canine nor the incisor had been
moved bodily and their apices remained in the original transposed relation. As
the result of traction to the ideally-placed bracket of the canine in a distal
direction, labial to the dental arch, the canine had become rotated 90 degrees
and its labial side palpably devoid of alveolar bony plate. The gingivae were
swollen and hemorrhagic and the head of the clinic where the child was treated
referred her to me with the expectation that the canine was no longer viable
and would need to be extracted (Fig. 5b). Orthodontic treatment had not been
performed in the maxilla.

Fig. 5c. The treatment direction was changed and the
lateral incisor was moved distally, to create space for the canine in the
transposed order between the lateral and central incisors.

It was clear at that point that correcting the transposed
order was only possible at extreme periodontal cost and the early extraction of
the canine. The only possible line of treatment that could be designed to save
the tooth would be to bring it into the alveolar bone as soon as possible. The
canine was freed from the existing distal traction elastic and its bracket
removed, to simplify oral hygiene, which had been largely ignored up to that
point. In order to achieve this without requiring the extraction of other
permanent teeth, the deciduous canine was extracted. The lateral incisor was
then pushed back distally into the healing socket area of the extracted
deciduous canine, to create space between it and the central incisor. The
canine was then realigned into the transposed order (Fig. 5c). At the same
time, orthodontic alignment and occlusal relations were corrected with the use
of a fixed multibracketed orthodontic appliance in the maxilla (Fig. 5d, e).

Fig. 5d. Occlusal and anterior views of the achieved
alignment at the completion of treatment shows considerable improvement in the
gingival condition of the canine, good alignment, but a long clinical crown in
comparison with the unaffected right canine.

Fig. 5e. Clinical views of the completed treatment on the
day appliances were removed.

So, what is the bottom line?

Whenever the labially impacted mandibular canine is impacted
on the mesial side of the lateral incisor, we are forced to move it “round the corner
in the outside lane” and its periodontal prognosis is poor. The orthodontist
who plans the treatment using the flat panoramic view alone, will fail to grasp
the hidden 3D factors that are at play in a curved archform and will likely
cause the treatment to fail. Impacted teeth within an expanding dentigerous
cyst or being pushed by a radicular cyst probably have greater powers of
resolution when the causative pathology has been eliminated, provided the
treatment is done early enough1. Extraction of deciduous canines and
premolars alone will probably not be useful preventive measures in the presence
of an enlarged follicle/dentigerous cyst, unless the cyst itself is also
evacuated.